This invention relates to apparatus for, and methods depositing sputtered atoms or molecules on substrates such as wafers for integrated circuit chips or magnetic transducer heads. More particularly, this invention relates to apparatus for, and methods of, controlling the characteristics of the depositions on such substrates.
Wafers are fabricated with a plurality of dies (sometimes as many as hundreds) on each wafer. Each of the dies on a wafer subsequently forms on integrated circuit chip. The dies are tested while on the wafer to determine if they have been produced properly. The defective dies are marked to distinguish them from the satisfactory dies. The dies are then cut from the wafer and the satisfactory dies are retained for use as integrated circuit chips.
The wafers are produced from a plurality of successive layers, some of electrically conductive material and others of electrically insulating material. When a layer of an electrically conductive material is formed, it generally is produced in a pattern to represent electrical circuitry. To produce this electrical circuitry, a layer of an electrically conductive material is initially deposited on the wafer, hopefully in a substantially uniform thickness. The layer is then masked with a material which is subjected to light in a pattern corresponding to the pattern of the electrical circuitry to be produced. The masking material subjected to the light is impervious to an etching material such as an acid.
The remaining portions of the layer are then etched as by an acid. The masking material subjected to the light is then removed from the remaining electrically conductive material in the layer. The electrically conductive material remaining in such layer, and in a plurality of other layers produced in the same manner, defines the electrical circuitry for each die on the wafer.
Apparatus has been in use for some time for depositing sputtered atoms on a wafer to produce a layer of material defined by the sputtered atoms. The apparatus now in use produces such a deposition by producing a glow discharge between an anode and a target in a cavity to obtain an emission of sputtered atoms from the target. A magnetic field co-operates with the electrical field to produce a force on the electrons for enhancing the movement of the electrons in the cavity between the target and the anode to facilitate the ionization of the neutral gas.
For example, when a layer of aluminum is to be deposited on a wafer, the target may be made from aluminum. When the target is bombarded with ions of an inert gas such as argon, the target emits sputtered atoms of aluminum. These atoms travel to the wafer and become deposited on the wafer to produce a substantially uniform layer of electrically conductive material on the wafer such as discussed in the previous paragraph. A water cooled, electrically biased shield may be disposed between the target and the substrate to inhibit charged particles in the cavity from reaching the substrate. These charged particles would otherwise impinge upon the substrate and heat the substrate, thereby causing the quality of the deposition on the substrate to deteriorate.
The apparatus now in use has certain disadvantages in depositing sputtered atoms on a wafer. One disadvantage is that the sputtered atoms are not always deposited in a substantially uniform thickness on the surface of the wafer. A further disadvantage is that the sputtered atoms are not deposited in a substantially uniform thickness on the walls of grooves in such wafer surface. This results from the asymmetrical disposition of the target relative to the walls of such grooves. This disadvantage has existed for some time in spite of the realization during such time of the existence of such disadvantage.
The apparatus now in use also has other disadvantages in depositing sputtered atoms on a wafer. The voltages on the shield and the magnetic members cause these members to attract electrons in the cavity. These electrons impinge on the shield and the magnetic members and heat these members. The shield and the magnetic members also receive depositions of stray sputtered atoms. The heat produced by the electron impingement on the shield and the magnetic members cause the depositions on these members to crack and to generate particles which can destroy electrical circuitry on the wafers.
Similar techniques to those discussed above are used to deposit aluminum oxide on a magnetic transducer head. For example, the sputtered atoms emitted from the target are combined chemically with oxygen introduced at a controlled rate into the cavity. The chemical combination causes aluminum oxide to be produced. The aluminum oxide is deposited on the magnetic transducer head. Aluminum oxide is advantageous because it is an electrical insulator and because it is hard. In this way, if the head should inadvertently contact an information medium such as a storage disc, the head will not be damaged mechanically and will no t be shorted electrically to the medium.
The apparatus used to deposit the aluminum oxide on the transducer head has certain significant disadvantages. One disadvantage is that the oxygen flow rate an d the voltage applied to the target are so critical that any relatively small change in these parameters causes the characteristics of the aluminum oxide deposited on the transducer head to change in an undesirable way. Specifically, the index of refraction of the aluminum oxide decreases to a value where the aluminum oxide becomes relatively soft. This causes the head to become damaged if the head should inadvertently contact the information medium.
In one embodiment of the invention, an electrical field between a positive anode and a negative target in a cavity and a magnetic field in the cavity cause electrons from the target to ionize a neutral gas (e.g. argon) atoms in the cavity. The ions cause the target to release sputtered atoms (e.g. aluminum) for deposition on a substrate. A shield between the target and the substrate inhibits charged particle movement to the substrate.
The anode potential may be positive, and the shield and the magnetic member s may be grounded, to obtain electron movement to the anode, thereby inhibiting the heating of the shield and the magnetic members by electron impingement. The anode may be water cooled. The magnitude of the positive anode voltage relative to the target voltage provides selectively for (a) a uniform thickness of sputtered atoms on the walls of a groove in the substrate or (b) a filling of the groove by the sputtered atoms and a uniform thickness of deposition on the substrate surface including the filled groove. Progressive differences in the anode-substrate voltage produce progressive increases in the rate at which the groove is filled by the sputtered atoms, and a uniform thickness of deposition is produced on the substrate surface including the filled groove.
Oxygen may be introduced into the cavity to combine reactively with the aluminum atoms and produce aluminum oxide. The oxygen flow into the cavity may be varied through a wide range at a substantially constant anode voltage to vary the refraction index between approximately 1.63-1.70 of the aluminum oxide deposited on the substrate. The oxygen flow rate may accordingly be selected to produce an acceptable aluminum oxide refraction index in the 1.63-1.70 range, without affecting the anode voltage, even with flow rate variations.